Qualifying days are days of experience that meet specific requirements for each rank of sailing or powerboat certification. The requirements are that you have experience on a boat (as crew or master) of a certain minimum size as well as master of the boat of a certain minimum size. Qualified Crew rank is exempted from any master of the boat requirements.
This all means that likely when you are operating a boat, you have some familiarity and confidence which leads to competence. Remember that the definition of competence is: Theory Knowledge, Practical Skills, and Experience.
SAIL Qualifying Days
See here for Bareboat Charter Master Qualifying days
See here for Offshore Captain Rank Qualifying days
See here for Skipper Large Sailboat Rank Qualifying Days
See here for Skipper Small Sailboat Rank Qualifying Days
See here for Qualified Crew Sailboat Rank Qualifying Days
POWER Qualifying Days
See here for Bareboat Charter Master Rank Qualifying Days
See here for Skipper Large Sailboat Rank Qualifying Days